During angioscopy, there are two problems which limit the potential utility of the procedure: 1) Although the vessel cross-section if visualized directly, unlike the case with angiography, the size of the cross-section can be assessed currently only subjectively, because (a) the size of the cross-section varies markedly with the lens-object distance, and (b) different portions of the circumference of a cross-section are often difficult to recognize as belonging to the same cross-section; and 2) The light source during endoscopic procedures is provided at the distal end of the fiberscope, and forward propagation of light down the lumen allows inspection, after displacement of blood by translucent crystalloids, of the luminal surface by light reflected back to the imaging fiberoptic bundle. However, the surface of proximal structures reflects light more strongly than distal ones (inverse square of distance relationship), resulting in excessive reflected light proximal to a lesion of interest.